APTT ratio
What it measures, and what changes the number.
The APTT ratio expresses the activated partial thromboplastin time as a comparison rather than in seconds. The lab divides the clotting time of the patient's plasma by the clotting time of a control plasma run with the same reagents, which makes results a little easier to compare across different reagent batches.
It is reported together with the APTT in seconds, and is usually read alongside prothrombin time, INR and prothrombin activity, which assess a different branch of the clotting cascade.
The same collection rules apply as for the APTT: a correctly filled citrate tube, prompt processing, and care to avoid heparin contamination. Because the reagent used for the test is sometimes called cephalin, Spanish-language labs may print it as Ratio de cefalina (APTT); it may also appear as APTT R or PTT ratio.
Often read alongside: APTT, Prothrombin time, INR, Prothrombin activity